GM 24936 is an attempt to seek out the functional component of excitable membranes which is most involved in the development of the surgical anesthetic state, and to use this component, if it exists, to test the concept of a direct antagonism between volatile anesthetics and high hydrostatic pressure. Such an antagonism is predicted from observations on intact animals in which pressure reverses the effects of anesthetics. We have studied certain firing patterns which occur spontaneously in central neurons of Aplysia californica as well as one electrically induced and several chemically activated changes in membrane potential. In every case which we have investigated halothane has caused a functional disruption but the application of 100 ATM hydrostatic pressure has failed to bring about a reversal of the anesthetic effect, or to restore the system to a functioning capacity. Thus we conclude, in the cases studied so far, that pressure reversal of anesthesia is not a general feature of narcosis and that direct site reversal by pressure is not a valid hypothesis to explain the observations seen with intact organisms.